Wow - I didn't realise how powerful these brushless motors can be

Regardless of the motor, battery cost and weight are still the limiting factors. 300W is about the high end of what makes sense with lipos. Above that, you're offsetting the weight and expense with noise and mess benefits. It's tough to beat a .61 for power density and low cost: 2 hp (1.5 kW), $150, 24 oz package. Engine/motor cost aside, fuel/batteries for a 5 minute flight (125 watt hours):

Nitro: 10 oz, $2.50. Lipo: 2100mAh 2s8p (12C): 50 oz, $550. NiMH: 35 3000 mAh (10C): 75 oz, $120.

But then, big electrics seem to be missing the point. Lightweight electronics and lightweight construction makes .15 size and smaller extremely attractive. Brushless and lipos do very well in that range.

Agreed, but electrics now can push over 500W/lb for the power train.

Your .60 is 24oz +10oz of fuel = a shade over 2lb for about 600W/lb

Basically you trade cost and flexibility of electric against cheap stink, noise and gunky exhaust and a motor that may quit on you when least expected. Your choice.

For big sport flyers glo has it, for comp work expect the ultra reliable throttling and cleaness of electric to make further inroads.

I'm not sure what that means. Is that motor and ESC weight alone, without batteries?

Depends on who you listen to. In nice round numbers, .60 is right around 2 hp on the shaft according to O.S., or 1492 watts. That would make it 750 W/lb. Without the fuel, to compare energy density, it's 1000 W/lb.

The economics are tough to generalize, and what makes sense depends very much on what you're doing. As they might say in a MasterCard commercial: "A few laps over and through your backyard to start your day. Priceless." For that, electrics stand alone in practicality and affordability. It's $5 for magnets to soup up the CD motor, a few feet of magnet wire, and then a stick and some glue for a motor mount. You're in the air for under $10. Almost. I forgot the big ticket items. Going cheap: $55 ESC; $50 charger; $30 battery. $10 in glue, tape, and house insulation; $50 for sub-pico rx and servos. Flying in style for $200 or less. Still absolutely priceless, not to mention the fun of returning to essentially grassroots.

What does it take to get to 300W? $100 for the ESC. $100 for the battery (or each battery, I should say). $120 for a small Hacker. $120 for a good charger. You won't be flying that in your backyard at any time, let alone in the still of dawn. Just the same, I would love to see how it livens up a 2 lb airframe. With a big fat NACA0020, the G's will probably pull the wings right off in turns. Still practical in its own way, if not exactly priceless. A rough running 10 year old .30 will put out the same 1/2 hp.

From there, it goes up steeply and incrementally. Dare I conjure up visions of wingtip extensions to carry the battery weight? I have a hard time guessing the numbers for 4 kW. I think it wins out over small gas turbines, though.

You left out something very important.. with batterys, a " refill costs pennies, not $2.50 again and agian and again.. The batterys ar good for 500 to 1000 cycles, so call it 750 cycles for a average at 1 minutes a flight. That would be 187.5 hours of flight.. Im asuming yo get 20 min on your 10 oz og glow fuel, so so that would 562. fillups at 2.50 562.5 x 2.50 = $1406.25.

so much for low cost. Over time the batterys will save you a fortune Even if you count up the pennies for charging, its still much cheape to go electric. Not to mention if you get more then the 15 minutes o flight or more then the 750 cycles, You are that much more ahead of th game. that extra 250 cycles alone is another 60 hours of fligh electric, or another 450 bucks if you fly glow. That alone will pay fo a decent charger, a extra brushless motor and controler.

Ken-Ohki " I make things do what I want them too, The Hell with what they ar designed to do.

-- Ken-Ohk

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Ken,

While your numbers are strictly true, you didn't pay cash for your house without saving up a lot of money. You had to have somewhere to live so you got a mortgage.

Same thing with glow vs electric. It takes a lot less initial investment to get flying with larger glow than with larger electrics. Gas can be bought over time as needed. Electrics need everything to be bought all up front.

Also, do the math with the cost of the fuel being around $1.00 for 10oz. That is more realistic. At that cost, it is only $562.00 for the fuel. And when the tank gets lower, there is less dead weight to carry around, unlike the batteries.

Also, for power density, a hot .46-50 is much better being in the 1.5-1.7hp range and weigning around 16oz.

Electrics are getting better, but they are still not an economic match for medium size glow engines.

View this thread:

Wow, I am so surprised that my original post started such a serious thread. I was KIDDING!! It was a tongue-in-cheek post when I read the specs on one of the motors listed on the site that I provided the URL for.

One of their motors was rated at 4200kva - that is FOUR MILLION TWO HUNDRED THOUSAND Watts

I emailed the guys there and pointed out their typo, so I presume they have fixed it by now.

David - who wonders if RC guys are always so serious

That's likely kV, RPM per volt. A low torque, high speed motor. Along with idle current and leg to leg resistance, the three simple numbers describe a motor's performance characteristics surprisingly well.

Without presuming to speak for others: Only when I can't go out to fly.

| You left out something very important.. with batterys, a "refill " | costs pennies, not $2.50 again and agian and again.. The batterys | are good for 500 to 1000 cycles, so call it 750 cycles for a average | at 15 minutes a flight.

NiCds are known to last up to 1000 cycles. NiMHs up to 500 cycles or so. LiPos, I'm not sure, but I doubt they last nearly as long as even NiMH cells. They also go downhill over time faster than NiMH or NiCd cells.

Note that these are full cycles (full charge to full discharge), and more like 1C discharge rates rather than 10C. I imagine that even 4C discharge rates would reduce their lifetime further.

| That would be 187.5 hours of flight.. Im asuming you get 20 min on | your 10 oz og glow fuel, so so that would 562.5 fillups at 2.50 | 562.5 x 2.50 = $1406.25.

I question that fuel price ...

One gallon of 10% nitromethane is around $13 around here. That's 128 fl oz, or 13 fill-ups of that fuel tank. So each fillup is about $1 rather than $2.50. Where did `Boat' get this $2.50 figure anyways?

So you're looking at $562 worth of glow fuel, but I don't think Boat's $550 LiPo pack (2100mAh 2s8p (12C) 50 oz, $550) will last as many cycles as you do. Also, Boat's calculation includes a 12C discharge rate (I checked his math -- it's accurate -- 12C at 3.7v on that battery pack gives 1492 watts, though we're ignoring any energy lost to a not 100% efficient motor.) How long will a 0.61 engine run at full throttle on 10 oz of fuel? Hopefully better than the less than 5 minutes that that battery pack will last at 12C.

| so much for low cost. Over time the batterys will save you a fortune.

Using your math and your 750 cycles estimate (which I question), the costs of the glow fuel vs. the LiPo battery are almost exactly the same ($550 vs $562) -- it hardly saves you a fortune.

To be fair, $550 seems a bit high for that battery pack. Using 18 10C rated IRATE-LP2200 cells at $18.50 fron CBP gives you similar performance, but only costs $333. Still, that's a lot to spend all at once. And you'll want at least two packs ...

That said, most of my flying is now either electrics or gliders. But it's a matter of convenience more than anything else -- I certainly don't think I'm saving a fortune. And I've ruined a *lot* more motors, ESCs and battery packs than glow engines in my flying `career'

-- if you ask me, electric flying costs more. But it's more fun. :)

No, with batteries.

No, keep the fuel on. PS its power diesnity - energy density is watt hours per lb.

Then its even stevens,because motore ESC and battery is not far off that these days. Plus the fact that unless you are flyig really fast planes, the IC engine will be devleping its power at an inappropiate RPM for the typical props, but the electric will be optimally geared, and the heavy prop and vibration of the IC make for a larger structural weight.

Unless you are flying lighweight ultra tuned 2 strokes, parity in terms of power to weight is avaialable these days, at a considerable price, but its there.

4KW in terms of battery is ot huge. Its a little over what most current motors will deliver...need to look at specialist manufactureres, but its only 40V/100A - not that hard to arrange. 12s5p of 2100 cells at $18 per cell - say around 1100 dollars of pack, and about 5lb in total weight for the pack. I think some of the bigher Actros/Lehners and maybe even hackers can absorb that kind of power. Probably another pound or two of motor...not quite man carrying power,but actually fairly close.

Which is merely to make the point that it all is possible with current gera, just very much not cheap.

>

Let's wrap this up, then. I made an assertion earlier that 300W was the cut off point where battery weight made nitro a better choice. Much higher than that, the battery weight so overwhelms everything that the motor might as well weigh nothing. I'm still trying to figure out what you mean by 500W/lb versus 600 W/lb for the powertrain.

The first raw cell I could point a web browser at is an E-TEC 1200 mAh HP (10C, $12.95, 25.7 grams). 3.7V, 12 A discharge rate, 17.65 to a pound ==>

784 W/lb for the first 10 minutes (and then 0 W/lb after). OK. With motor and controller, and considering efficiency, it's in the 500 W/lb range. I think I see where you're coming from.

For 300W, you need 6 oz. of battery. That's reasonable, and pretty close to what nitro fuel weighs.

For 1500W, you need almost 2 lbs of batteries. That's do-able, but very punishing.

With nitro,

Tower, 30% 4-gallon case price: $90 plus shipping, hazmat, and IL sales tax. $30 a gallon. Rounding up because I felt generous. It's a verifiable worst case number.

330 or so cycles, from a manufacturer's white paper. I think it was Kokam, but could just as easily have been Thunder Power or ETec. Also talked about capacity with regards to cycle age and discharge rate. Interesting reading, but not much more info than what we already know. I can't find the link this moment.

The problem isn't strictly the cost. Battery weight for .30 and larger becomes prohibitive. Power density for lipos is very close to 1 hp/lb at

10C, a pair of very round numbers you can easily roll off the top of your head.

Boat,

30% fuel is way out of the norm for average .60 engines. 5-10% is the best range. With 30% nitro, I could push a 2lb YS .91 to near 3hp.

It's an extreme worst case number. You don't buy fuel from Tower unless you have *no* other choice -- the hazmat fees eat you up, and the shipping doesn't help unless you can avoid sales tax.

You also didn't really round up. $90 for the 4 gallons, $20 hazmat fee per case (yes, that is the real cost), $8 shipping, $7 sales tax (I assume it doesn't apply to the hazmat fee). $31.25/gallon, to your door.

The rest of the US buys 10% nitro for about $13/gallon, and many people buy it in bulk (or mix their own) for less. If you reduce the nitro percentage, it gets even cheaper.

And as Paul said, 30% nitro is the exception rather than the norm. The only people I know that use 30% nitro are helicopter guys and car racers.

| > | so much for low cost. Over time the batterys will save you a fortune. | >

| > Using your math and your 750 cycles estimate (which I question), the | > costs of the glow fuel vs. the LiPo battery are almost exactly the | > same ($550 vs $562) -- it hardly saves you a fortune. | | 330 or so cycles, from a manufacturer's white paper.

I believe that. It totally blows away the `electric is much cheaper' argument -- instead of $550 (electric) vs $562 (glow), using 330 cycles and the cheaper battery pack that I mentioned earlier, it turns into $750 (electric) vs. $562 (glow) for the same 180 hours or so of flight time mentioned earlier. These are probably typical values -- if one has a cheaper than retail source for glow fuel or batteries, both figures could easily go down.

(Also note that we're still assuming 100% efficient motors and gear boxes.)

| I can't find the link this moment.

If you do, post it. It's probably something many of us want to read. | The problem isn't strictly the cost. Battery weight for .30 and larger | becomes prohibitive. Power density for lipos is very close to 1 hp/lb at | 10C, a pair of very round numbers you can easily roll off the top of your | head.

I think it's mostly the cost. For sport flying, that 1 hp/lb at 10C is plenty.

Yes, if I were serious about pylon racing, I'd probably go with glow, and certainly if I had some plane that I meant to fly for hours without refueling, but beyond that, the only thing keeping me from going 100% electric is cost :)

(and it's not even the cost of ESCs and brushless motors anymore. It's the cost of *batteries*.)

You still stand a far greater chance of getting sliced by the prop of a glow engine than you do an electric:

1. Mishaps during starting, even using a chicken stick or electric starter.
2. Mishaps during tuning, even with a remote needle valve.
3. Mishaps during moving the running plane from bench to taxiway, or pit to runway, or any combination.
4. Mishaps due to the engine not shutting down after the flight.

None of these risks are present on an electric airplane in most plausible situations, where they exist in EVERY plausible situation that involves a glow engine...

I'm not completely sure I agree. I've got three prop scars -- one from glow, and two from electrics.

| 1. Mishaps during starting, even using a chicken stick or electric | starter.

That's where my glow scar came from. 1.20 sized Saito got stuck where the starter couldn't move it, so I went to turn it by hand past the tough part. Forgot that the glow ignitor was still on, and it backfired even though I had a good grip on the prop. Cut my finger nicely, doing a little nerve damage. I certainly should have known better, but I certainly do now.

Ironically, I haven't flown the plane since, and it's been like two years. Still has some of my blood on it too.

| 2. Mishaps during tuning, even with a remote needle valve. | 3. Mishaps during moving the running plane from bench to taxiway, or | pit to runway, or any combination.

These can happen with electrics too. You may want to taxi to the runway, or it may roar to life while you're holding it, which is how I got my second electric scar.

My first electric scar happened while putting a plane together, on the bench. I thought `let's hook this up' ... bam!

| None of these risks are present on an electric airplane in most | plausible situations, where they exist in EVERY plausible situation | that involves a glow engine...

I do think that electrics are generally safer, because you don't have to muck with them as much, but let's not delude ourselves into thinking that they don't roar to life unexpectedly, because they do.

If the battery is hooked up, or if you're not sure if the battery is hooked up or not, assume that it could go to full throttle at any time, and therefore keep it pointed away from you with the prop not near anything. If you're working on the plane and it needs to be powered up, remove the prop if you can.

True, but then you don't normally have to flick and fiddle in the vicinity of the electric prop, so i'd say safety wise there is little in it.

The moment the battery is connected, my electric motor is 'started' safety wise.

However most modern ESC's need a 'zero throttle for a second,full throttle for a second, zero throttle for a second' start up sequence, which makes it extremely unlikely that you will get a false start unless you already armed the plane.

Huh? Not compared with the weight of an equivelent glo engine, no.

Ate you saying you can get a 2bhp engine under 2lb in weight? That delicvers that 2bhpo not into a dyno at 26000 RPM but into a prop doing

7000 RPM?

Power density for lipos is very close to 1 hp/lb at

yes.,